This invention relates to an improvement of a vane pump utilized for a power steering device for decreasing a handle steering power of a motor car, for example.
In the oldest type of the vane pump, a cam ring containing a rotor provided with vanes slidable in the radial direction is clamped between pump bodies. With this construction, however, the bodies undergo deformation as the pump discharge pressure increases to increase the clearance between the pump bodies and the cam ring thereby causing internal leakage and decrease in the pump efficiency.
To solve this problem, according to a vane pump of this type, a pair of plates are provided on both sides of the cam ring to form a set of pump cartridge which is incorporated into the pump bodies. Furthermore, a high pressure chamber subjected to the pump discharge pressure is provided on the outside of our plate so as to urge the plate against the cam ring by the fluid pressure to decrease the clearances between various members to values less than a definite value. Such pump is called a pressure loading type pump.
However, the vane pump of the pressure loading type requires the pair of plates described above, a spring for holding the plates and sealing member for sealing various members. Thus, this type require a large number of component parts and its construction is complicated so that the size and weight of the pump increase and the manufacturing cost is high.
These problems counteract energy saving which is strongly desired in recent years. More particularly, the vane pump of this type is susceptible to such limitations that it is installed in a narrow space of an engine room, and that it has an influence upon the cost and weight of a motor car. Accordingly, it has been desired to provide a vane pump having smaller size and weight and which can be manufactured at lower cost than the prior art vane pump. In recent years, power steering apparatus are used even in small motor cars so that the requirement described above becomes more universal.
Accordingly, in recent years the vane pump whose discharge pressure may be low is not constructed as the pressure loading type and a pair of plates on both sides of the cam ring are not used, but instead the cam ring is directly held between the pump bodies. One example of such a pump is disclosed in Japanese Laid Open Patent Specification No. 69491/1981. In the vane pump disclosed in this laid open patent specification, a cam ring having a substantially elliptical shape and adapted to contain a rotor has an external shape the same as that of the pump bodies connected to both sides of the cam ring, and a fluid passage for conveying pump suction side fluid from one body to the other is formed through the cam ring. Further, sealing grooves for receiving sealing members for preventing leakage of the operating fluid are formed on both side surfaces. Accordingly, the shape of the vane pump is complicated and difficult to machine. Especially, when the cam ring is made of a high grade alloy casting its cost and weight are large. Where sintered material is used the fluid in the pump has a tendency to leak.